Turkish Foreign Minister Mevlut Cavusoglu has denied that Turkey is delaying the purchase of S-400 missile defense systems from Russia amid tensions with the United States.

Cavusoglu told reporters on Wednesday that “there is no question of any delay or of any halting at this point.” He reiterated that Turkey’s purchase of the Russian-made systems is a “done deal.”

The issue has caused a deep rift with the United States, which says the Russian missiles pose a threat to the U.S. F-35 fighter jet program of which Turkey is also a partner. Media reports suggested Turkey would delay the purchase.

Cavusoglu said Turkey and the United States were discussing a Turkish proposal for the establishment of a joint committee to review the S-400s possible risks to the U.S. F-35 program.